Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 131141
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
541 AM CST SAT DEC 13 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 447 AM CST SAT DEC 13 2014

STRATUS/FOG/DRIZZLE...AND ASSOCIATED EFFECT ON TEMPERATURES...
CONTINUE TO BE PRIMARY CHALLENGE FOR THE FIRST 24 HOURS OF THE
FORECAST. AFTER DECENT BOUNDARY LAYER MIXING FRIDAY AFTERNOON
SCOURED OUT SOME OF THE LOW LEVEL MOISTURE...STRATUS HAS BEEN SLOW
TO EXPAND BACK TO THE NORTH THROUGH THESE EARLY MORNING HOURS.
STARTING TO SEE SOME NORTHWARD PUSH OVER THE LAST HOUR OR TWO
THOUGH...SO WILL CONTINUE IDEA OF EXPANDING CLOUD COVER ESPECIALLY
EAST OF THE JAMES RIVER VALLEY THROUGH MID MORNING...THEN ERODING
FROM THE WEST TO NEAR I-29 CORRIDOR BY MID AFTERNOON WHILE CLOUDS
REMAIN A BIT MORE PERSISTENT EAST OF KYKN-KFSD-KBKX LINE. MOISTURE
LAYER REMAINS FAIRLY SHALLOW THROUGHOUT THE DAY...SO THINK DRIZZLE
POTENTIAL IS MINIMAL AND HAVE REMOVED MENTION UNTIL THE MID-LATE
EVENING HOURS WHEN SOUNDINGS BEGIN TO SHOW DEPTH OF MOISTURE LAYER
INCREASING TO NEAR 850MB. NOT OVERLY EXCITED ABOUT POTENTIAL FOR
TRUE RAIN THROUGH TONIGHT...AS JUST REALLY DO NOT HAVE MOISTURE
AVAILABLE ABOVE THE STRATUS LAYER TO PRODUCE LARGER DROP SIZES.
HOWEVER...WITH SOME DEEPER STRATUS LAYER AND INCREASE IN WARM
ADVECTION AFTER 06Z TONIGHT...CERTAINLY CANNOT RULE OUT MORE
PERSISTENT DRIZZLE PRODUCING A HUNDREDTH OR TWO SO WILL KEEP SOME
LOW MEASURABLE POPS FOR THE EASTERN 2/3 OF THE FORECAST AREA LATE
TONIGHT.

TEMPERATURES TODAY ALREADY STARTING OFF MILD WITH MID 30S TO LOWER
40S IN CLEAR AREAS...AND MID 40S TO NEAR 50 BENEATH THE STRATUS IN
OUR SOUTHEAST. IF STRATUS DOES PERSIST ACROSS NORTHWEST IOWA AS IS
CURRENTLY EXPECTED...WILL LIKELY NOT SEE READINGS MOVE MORE THAN A
FEW DEGREES THROUGHOUT THE DAY...WHILE AREAS FARTHER WEST SEE MORE
OF A REBOUND INTO THE MID TO UPPER 50S. CONTINUED SOUTHERLY FLOW OF
MOISTURE TONIGHT SHOULD HOLD READINGS UP IN THE MID TO UPPER 40S
OVER MUCH OF THE AREA...THOUGH FAR WESTERN AREAS WILL DIP DOWN INTO
30S AS COLD FRONT APPROACHES BY 12Z.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 447 AM CST SAT DEC 13 2014

FRONTAL BOUNDARY WILL TRUDGE ACROSS THE CWA ON SUNDAY WORKING TO
DISPLACE THE DEEP SOUTHERLY FLOW AND MILD TEMPERATURES...AT LEAST
THROUGH THE LOWER LEVELS. AHEAD OF THE FRONT...DEWPOINTS WILL BE
IN THE UPPER 40S TO LOWER 50S...ALONG WITH A THREAT FOR FOG...
STRATUS AND AREAS DRIZZLE. THE CHANCE FOR ACTUAL RAINFALL WILL
INCREASE TO MORE THAN TRIVIAL DURING THE MORNING AND ESPECIALLY
THE AFTERNOON AS MOISTURE DEEPENS WITH FIRST BIT OF MID LEVEL
INTRUSION. TEMPS AHEAD OF THE FRONT WILL TRACE CLOSELY WITH
DEWPOINT READINGS...BUT AFTER SOME MIXING HELP AND PERHAPS A
LITTLE BIT OF CLEARING NEAR AND THE BOUNDARY WHICH WILL PUSH EARLY
DAY TEMPS UP ACROSS THE WEST IN THE MORNING...THE VERY STRONG SUB
900 HPA THERMAL ADVECTION WILL START TEMPS HEADING IN THE NON
DIURNAL DIRECTION. AS NEGATIVE TILT TROUGH PUSHES OUT INTO THE
SOUTHERN HIGH PLAINS...EVOLVING FROM THE CURRENT CALIFORNIA
STORM...BOUNDARY SHOULD START TO SLOW UP...AND Q VECTORS SUGGEST
THAT THE SLOWER PROGRESSION PER GFS/CANADIAN WOULD BE THE WAY TO
HEDGE AT THIS POINT. NONETHELESS...TEMPS SURFACE AND ALOFT REMAIN
TOO WARM THROUGH SUNDAY...EVEN IN THE WEST...FOR ANYTHING BUT A
LIQUID THREAT.

SIGNIFICANT WINTRY SYSTEM SUNDAY NIGHT THROUGH MONDAY NIGHT IS
THE PRIMARY FOCUS OF THIS FORECAST. OVERALL...MODELS ALL ARE
FOLLOWING THE SAME PLAYBOOK...BUT CALLING DIFFERENT PLAYS AS
SOUTHERN STREAM NEGATIVELY TILTED CLOSED LOW PULLS NORTHEAST AND
PHASES INTO NORTHERN STREAM SOMEWHERE TOWARD THE GREAT LAKES.
PROGRESSION OF THE BAROCLINIC BOUNDARY AT MANY LEVELS...AND
FAVORED QPF AXIS STILL EXHIBIT A GREAT VARIATION...DESPITE MASS
FIELDS BEING FAIRLY SIMILAR. DEEPENING SYSTEM TO THE SOUTH WILL
HELP TO PULL COLD AIR IN AT THE LOWEST LEVELS BEHIND THE FRONTAL
BOUNDARY WHICH WILL SLOW/STALL VERY NEAR THE FAR SOUTHEASTERN CWA
THROUGH EARLY MONDAY. MEANWHILE...THE COOLING ALOFT WILL OCCUR AT
A MUCH LESSER RATE...WITH OUR LINGERING WEDGE OF VERY WARM AIR
SLOWER TO DISPLACE AS FLOW KEEPS A BIT MORE SOUTHERLY/EASTERLY
COMPONENT.  WHILE MUCH OF THE AREA WILL START PRECIP FREE TOWARD
THE NORTH/WEST CWA...PRECIPITATION WILL BEGIN TO DEVELOP SUNDAY
NIGHT BACK TOWARD THE MID LEVEL BOUNDARY ACROSS WESTERN AND
CENTRAL SD AS NORTHERN STREAM JET BEGINS TO INCREASE ACROSS NORTH
DAKOTA. APPEARS THAT MOST SIGNIFICANT PRECIPITATION WILL HOLD OFF
UNTIL AFTER 06Z MON AS FIRST LOBE OF DIV Q WRAPS NORTH OUT OF
NEBRASKA ON NOSE OF MID LEVEL DRYING...PRIMARILY SOUTH OF I-90 BY
DAYBREAK. THIS WILL PLACE PORTIONS OF THE AREA IN GREATER JEOPARDY
OF FREEZING RAIN OR SLEET BETWEEN THE JAMES AND I29 AND INTO SW MN
BY DAYBREAK...AND ESPECIALLY DURING THE MORNING EAST SW MN AND
NORTHERN NW IA...BACK INTO FAR EASTERN SD AS THE PUSH OF UPPER
WAVE TO THE SOUTHEAST HOLDS BACK THE WARMER AIR ALOFT WHILE
PRESSURE FALLS TO THE SOUTH INCREASE THE LOWEST LEVEL NORTHERLY
FLOW. GRADUALLY THE COOLING ALOFT WILL SLIP EASTWARD AND
TRANSITION WINTRY MIX OVER TO SNOWFALL...BUT THIS WILL BE A
CHALLENGE TO REACH THE FAR SOUTHEAST DURING THE DAY AS ICE
BEARING TEMPS FLIRT ALONG EDGE OF DRY SLOT.

HARD TO GET BOGGED DOWN ON DETAILS YET AT THIS POINT WITH SO MUCH
UNCERTAINTY ON TYPE/TIMING....BUT THE OVERALL MESSAGE AT THIS
POINT IS FOR A SIGNIFICANT WINTER WEATHER SYSTEM ACROSS THE
AREA...FEATURING POTENTIAL FOR AREAS OF SW MN...EXTREME NW
IA...AND EASTERN SD TO GET SOME FAIRLY SIGNIFICANT ICE
ACCUMULATION /UP TO A COUPLE TENTHS OF AN INCH IN PARTS OF SW MN
AND NW IA/...WITH THEN AN AREA OF SNOW FROM 3 TO 6 INCHES TO THE
NORTHWEST OF THE GREATER ICE THREAT FOR MUCH OF SE SD TOWARD
NORTHERN PORTIONS OF SW MN. MUCH WILL DEPEND ON WHERE THE MID
LEVEL DEFORMATION SETS UP NORTH BETWEEN THE SOUTHERN AND NORTHERN
STREAM SYSTEMS...AND RELATIVE STRENGTH OF THE TWO COMPONENTS
REMAINS IN FLUX AS DOES THE NORTH/SOUTH LOCATION OF HEAVIER SNOW
BAND. AT THIS TIME...HAVE COORDINATED TO NOT ISSUE ANY WINTER
WEATHER HIGHLIGHTS. EVENT IS LARGELY 36 TO 48 HOURS OUT...AND
REMAINS A WIDE RANGE QPF LOCATION AND MESSY TYPE CONCERNS. WOULD
EXPECT THAT THERE WILL BE AN EVENTUAL NEED FOR WINTER HEADLINES IN
MUCH OF THE AREA.

AFTER LINGERING BAND OF SNOWFALL TAPERS OFF ON MONDAY EVENING WITH
PERHAPS ANOTHER INCH OR SO ACCUMULATION FROM AROUND KFSD NORTH AND
EASTWARD...SETTLE INTO A MUCH COOLER PATTERN FOR THE UPCOMING
WEEK. LONG RANGE MODELS CONTINUE TO BE QUITE DIVISIVE ON LARGER
SCALE MIDWEEK...BUT MORE AND MORE LOOKS AS IF THE ECMWF IS THE ODD
MODEL OUT ALLOWING SUCH STRONG SHORT WAVE RIDGING...BUT FAR MORE
REASONABLE THAN THE GFS AND THE RETROGRESSION OF NORTHERN STREAM.
THE 06Z GFS IS CERTAINLY WORKING TOWARD A MORE REASONABLE LOOKING
SOLUTION COMPARED TO 00Z RUN...COMPARABLE TO CANADIAN. MAINTAINED
SOME VERY LOW THREAT LIGHT SNOWFALL CHANCES FOR WED NIGHT INTO
THURSDAY TO ACCOUNT FOR BROAD LIFT WITH WEAK TROUGHING.
OTHERWISE...DID PUSH MANY TEMPERATURES DOWN SOMEWHAT WITH COLDER
LOW LEVEL AIRMASS AND EXPECTED SNOW COVER.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 541 AM CST SAT DEC 13 2014

PERIODS OF MVFR-LOCALLY IFR CONDITIONS EXPECTED ACROSS THE REGION
THROUGH TONIGHT. LOW CEILINGS WILL BE MOST PREVALENT SOUTH THROUGH
EAST OF KFSD...WHILE LOCATIONS WEST OF KFSD WILL BE MOST LIKELY TO
SEE VFR CONDITIONS DOMINATE THROUGH AT LEAST EARLY THIS EVENING. A
CONTINUED INFLUX OF LOW LEVEL MOISTURE SHOULD RESULT IN A WESTWARD
EXPANSION OF MVFR CONDITIONS INTO AT LEAST THE JAMES RIVER VALLEY
TONIGHT...WITH THICKER STRATUS DECK ALONG/EAST OF US HIGHWAY 81
LEADING TO POTENTIAL FOR DRIZZLE. MILD TEMPERATURES EXPECTED WITH
MORE EXPANSIVE STRATUS...SO ICING DUE TO ANY LIGHT PRECIPITATION
IS NOT ANTICIPATED.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
&&

$$

SHORT TERM...JH
LONG TERM...CHAPMAN
AVIATION...JH



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